In this age of environmental awareness, it has become increasingly more important to study the chronic effects of a variety of pollutants and concentrations thereof on resident marine organisms, especially in pollutant-impacted harbor environs. Simulation of chronic effects are best achieved by flow-through bioassay testing procedures. Simply defined, these procedures provide for a long term (several months) constant flow of pollutants in a controlled marine environment. Typically, outdoor aquaria (or microcosms as they are known) of about 30 to 100 gallon volume are used to simulate the marine ecosystems because of their ability to maintain low to medium diversity assemblage of aquatic organisms for periods of several months.
The microcosms are provided with continuous flowthrough of unfiltered seawater and are exposed to normal sunlight. As such, they are linked energetically to the natural world, receiving input of ambient sunlight and nutrients, and can be colonized by larval organisms present in the supply water. In microcosms, many organisms can subsist on available natural foods and can experience near-natural seral development and growth. It is being increasingly recognized that chronic studies performed under such conditions provide a more realistic test of overall toxicity and bioaccumulation of pollutants than tests performed in static setting. Furthermore, extreme variability of concentrations of dissolved toxins, commonly experienced in static tests due to intank degradation and absorption of toxin, is large avoided by continuous addition of toxin to water of flowthrough tests.
Conventional valved systems are unreliable for long-term, precise flow control of unfiltered seawater supplies because valve orifices are easily obstructed by biofouling and other debris. Where seawater is being pumped from high fouling/high sediment environments, valves and piping must be cleaned at least daily to avoid flow alterations. Bioassay diluters of the Mount-Warner-Brungs type, which use automatic siphon tubes and narrow venturi tubes for water delivery and dilution, are suitable only for controlling low flows of filtered water. Some bioassay diluter systems utilize metering devices such as syringe pumps and peristaltic pumps to add toxicant solutions to supply waters of individual tanks. Such systems are prone to frequent malfunction and must be closely monitored for wear of materials such as syringe o-rings and peristaltic tubing.
Alternatively, high precision pumps may be employed to maintain a constant flow rate. However, these pumps are expensive and are costly to maintain in high sediment/fouling environments. Furthermore, most bioassay testing operations utilize a plurality of test aquaria thereby requiring several pumps. Thus, a need exists for a flowthrough apparatus that can provide a constant flow of ambient or pollutant-tainted waters to test aquaria without relying on valves or expensive pumps as a primary means of flow rate control.
Therefore, an object of the present invention is to provide a flow control and diluter system that can be used in bioassay testing. Another object of the present invention is to provide a flow-control and diluter system capable of delivering a controlled flow of seawater/pollutant dilutions to a plurality of experimental test aquaria at selected constant flow rates. A further object of the present invention is to provide a flow control and diluter system capable of delivering a controlled flow of seawater/pollutant dilutions over long periods of time while being free of system fouling concerns. Yet another object of the present invention is to provide a flow control and diluter system capable of delivering a controlled flow of seawater/pollutant dilutions even when the seawater generates high levels of biological and/or sediment fouling in the bioassay system. Still another object of the present invention is to provide a flow control and diluter system that is adaptable to a portable design.